The semiconductor integrated circuit (IC) industry has experienced exponential growth. Technological advances in IC materials, and processing operations have produced generations of ICs where each generation has smaller and more complex circuits than the previous generation.
ICs are formed on wafers, which must go through hundreds of processing steps, each of which is typically performed in a process chamber of a wafer processing tooling specially designed for the particular process, in many cases, under a vacuum or near-vacuum condition. Typically, the wafers are automatically transported from one wafer processing tooling to another by a wafer transfer system called an automatic material handling system (AMHS), while being contained in a wafer carrier called a front opening unified pod or a front opening universal pod (FOUP). A FOUP is a specialized plastic enclosure designed to hold silicon wafers securely and safely, and to allow the wafers to be removed for processing or measurement into a wafer processing tool equipped with appropriate load ports and robotic handling systems. A typical FOUP contains about 25 wafers of 300 mm diameter that are held securely by fins in the FOUP, and has a front opening door to allow robot handling mechanisms to access the wafers.
The sealing system of the currently used FOUPs is not adapted to provide and maintain any vacuum or pressurized environment to the wafers, and so, the wafers are kept in the FOUPs under an atmospheric pressure. This may result in problems such as allowing moisture and/or chemicals to enter into the FOUPS, which may contaminate the wafers.
To prevent such a potential wafer contamination, therefore, it is desirable to provide a wafer carrier, which can provide a constant preset pressure to the wafers therein during transportation, a pressure either lower or higher than the atmospheric pressure depending on a particular need. And it is further desirable to provide an improved system and method of transferring wafers that can, by utilizing such a pressure-controlled wafer carrier, not only eliminate the wafer contamination problem, but also reduce the wafer transfer time, the time spent for a wafer carrier to move between two neighboring wafer processing tools.